Monkey See, Babies Do - At 6 Months

One of life's toughest lessons is coming face to face with our diminishing abilities, but few of us suspect that day can come at age 9 months.

Even at that tender age, babies can no longer pick out individual monkey faces from a lineup with the same ease they did just three months earlier, researchers in England and at the University of Minnesota recently reported in the journal Science.

During that three-month period, the infants' ability to identify particular monkeys is relegated to the neurological trash can as they learn to specialize in telling human faces apart, the researchers concluded.

"It's like learning to distinguish between different species of birds or different models of cars," says Charles Nelson, an author of the study and co-director of the Center for Neurobehavioral Development at the University of Minnesota. "We're not born with the ability to do it - just the ability to learn to do it."

And we are born, apparently, with a tendency to get set in our ways of perceiving things as we age. The Science study illustrates the principle of "perceptual narrowing," the idea that aging brains jettison unneeded stimuli and encode more pertinent information.

"We usually think about development as a process of gaining skills, so what is surprising about this case is that babies seem to be losing ability as they age," says Michelle de Haan, of the Institute of Child Health at the University College London and an author of the study.

Adults have a harder time distinguishing between faces of people of races other than their own, while younger children show no such deficit.

Similarly, it is well-established that the young pick up foreign languages more quickly than adults; however, few people are aware that language skills start slipping even before infants hang up their Pampers. Nelson notes one study showed that 6-month-old infants distinguish sounds in any language, but by 9 months babies have begun to specialize in distinguishing sounds of their native language.

The researchers suggest that the developing brain fine-tunes its ability to perceive speech and faces between 6 months and 9 months of age.

So how do scientists measure recognition in infants whose vocabulary is limited to "Dah-Dah"?

The authors of the Science paper exposed 11 adults, 30 9-month-olds and 30 6-month-olds to faces of both monkeys and people. Then they showed the subjects pairs of pictures of monkeys and pairs of pictures of people. A picture of one individual in each pairing of monkeys or people had been shown to the adults and babies before.

If a study subject spent more time looking at the unfamiliar photograph, then he or she was deemed to have recognized the face already seen.

The 9-month-old babies and the adults took much longer to examine new human faces. However, they looked at the monkey faces an equal amount of time, indicating that they failed to distinguish between familiar and unfamiliar monkeys.

Six-month-old infants, however, spent a longer time studying both the new monkey faces and the new human faces - indicating that they recognized the monkeys they'd seen before.

Adults and over-the-hill 1-year-olds should take heart, the researchers said. Their shortcomings in perception seem to be a part of development, not linked to declining memory or learning skills. And with practice, most people can learn new perceptual skills and languages.